Add more metadata to records

[nuest]

See the updated Zenodo curation policy which now also mentions alternative identifier and relationships: https://zenodo.org/communities/codecheck/curation-policy

Example record: https://zenodo.org/records/14576035

This needs to be added for all historic certificates! Grunt work 😓

Related to #109 - if and when we go to the lengths to update old metadata, we should do it once with as many changes that we can imagine, or script it!